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The difference between DC contactor and AC contactor

Dec 16,2021 | simplybuy industrial

1. AC contactor adopts grid plate arc extinguishing device, while DC contactor adopts magnetic blowing arc extinguishing device.

2. The starting current of the AC contactor is large, and its operating frequency is up to about 600 times/h, and the operating frequency of the DC contactor can reach up to 1200 times/h.

3. The iron core of the AC contactor will produce eddy current and hysteresis loss, while the DC contactor has no iron core loss. Therefore, the iron core of the AC contactor is made of laminated silicon steel sheets that are insulated from each other, and is often made into an E shape; the iron core of the DC contactor is made of a whole piece of mild steel, and most of them are made into a U shape.

4. Since the AC contactor passes single-phase AC power, to eliminate the vibration and noise generated by the electromagnet, a short-circuit ring is embedded on the end face of the static iron core, while the DC contactor is not required.

5. The AC contactor can be substituted for the DC contactor in an emergency, and the pull-in time cannot exceed 2 hours (because the heat dissipation of the AC coil is worse than that of the DC, which is determined by their different structures). It is best to use it for a long time. There is a resistor in the AC coil, but DC is not a substitute for an AC contractor.

6. The number of coil turns of the AC contactor is small, and the number of coil turns of the DC contactor is large. The volume of the coil can be distinguished. In the case of excessive current in the main circuit (Ie>250A), the contactor uses series double windings. Coil

7. The reactance of the coil of the DC relay is large and the current is small. If it is said that it will not be damaged if it is connected to AC power, it is time to release it. However, the reactance of the coil of an AC relay is small, and the current is large. If it is connected to a direct current, the coil will be damaged.

8. The AC contactor has a short-circuit ring on the iron core. In principle, there should be no AC contactor on the DC contactor. The iron core is generally laminated with silicon steel sheets to reduce the eddy current and magnetism generated by the alternating magnetic field in the iron core. Hysteresis loss to avoid overheating of the iron core. The iron core in the DC contactor coil does not generate eddy currents, and the DC iron core does not have the problem of heating, so the iron core can be made of monolithic cast steel or cast iron. The coil of the DC circuit has no inductive reactance, so the coil has a large number of turns, large resistance, and large copper loss. Therefore, the heating of the coil itself is the main thing. To make the coil have good heat dissipation, the coil is usually made into a long and thin cylindrical shape. The coil of the AC contactor has few turns and low resistance, but the iron core generates heat. The coil is generally made into a thick and short cylindrical shape with a certain gap between it and the iron core to facilitate heat dissipation and at the same time prevent the coil from being burned out by heating. . To eliminate the vibration and noise generated by the electromagnet, the AC contactor has a short-circuit ring embedded on the end face of the static iron core, while the DC contactor does not need a short-circuit ring.

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